This invention relates to improved lithographic printing plates and a novel method for their preparation. More particularly this invention comprises an aluminum based lithographic printing plate prepared by exposing an aluminum base sheet upon which has been coated, either separate layers or in an admixture, a lithographically suitable light sensitive diazo compound and a photopolymerizable composition, to radiation through a mask or transparency, developing said exposed plate and finally post-curing said developed plate by exposure to high intensity radiation or air-baking at high temperatures.
It is well recognized that a substantial amount of lithographic printing plates are prepared by exposing an aluminum based photosensitive plate composition to radiation, developing said exposed plates and post-curing the developed plates by further exposure to the first radiation source for longer periods of time.
Among the disadvantages of plates of this type are short press lives, low image durability and resolution.
The instant invention provides an improved lithographic plate and a method for its preparation wherein a photosensitive plate, after exposure through a mask or transparency and development is post-cured by short-term exposure to high intensity radiation or air-baking at elevated temperatures. The resulting lithographic printing plates demonstrate long press lives and high image durability and resolution.